1. Field of the Invention
The invention relates to cooling a surgical incision in the human eye to prevent excessive temperature elevation within the incision from use of a vibrating, ultrasonic needle of a surgical instrument. Fluid flows through an infusion sleeve to travel across valley formations at the distal end of the sleeve to cool the incision.
2. Discussion of Related Art
A common method of cataract removal requires the use of a vibrating ultrasonic needle that can be inserted through a small incision in the human eye. The vibrating needle can cause temperature elevation within the incision. This temperature elevation is a problem that requires certain protective mechanisms, that is, precautions and/or technologies, in order to reduce the possibility of creating a thermal injury to the surrounding ocular tissues. Such protective mechanisms include the creation of an incision which is substantially larger than the ultrasonic needle or probe, with resultant leakage of fluid from the eye around the vibrating tip serving as a coolant. Other protective mechanisms include those previously devised by the applicant, and include the use of a rigid sleeve inserted between the vibrating needle and the soft, pliant outer sleeve through which infusion is delivered into the eye, or the use of an optical pachymeter to monitor the temperature in the vicinity of the ultrasonic needle or probe and discontinue needle or probe vibration in the event of undesirable temperature elevation.
Recently, there has been interest in performing ultrasonic removal (phacoemulsification) of human cataracts in a manner which divides the location of the entry of the infusion source and the ultrasonic needle into the eye into two smaller incisions in the eye. However, there has been concern that the use of a “bare” ultrasonic needle could increase the risk of thermal injury to the surrounding tissues because of the absence of surrounding infusion sleeves and the fluid contained within such infusion sleeve(s) that normally serve as coolants. It has therefore been advocated and it is the current practice to employ a method in which the surgical incision for insertion of the ultrasonic needle or probe be made substantially larger than that required for insertion of the needle or probe in order to permit fluid leakage from inside the eye to leak alongside the ultrasonic needle and thereby cool the latter.
While such a method will undoubtedly reduce the temperature of the needle, it is not desirable to have fluid leakage from the eye as this increases the trauma inflicted by fluid circulating through the eye during the procedure (a greater amount of fluid passes through the eye during the procedure), control of the pressure within the eye can be compromised by the leakage and this can lead to collapse of the eye, such collapse leading to contact of the vibrating ultrasonic needle with delicate ocular tissues such as the iris, cornea or lens capsule.
It has been the experience of applicant, who has performed tens of thousands of ultrasonic cataract extractions, that the greatest risk of thermal injury occurs at the external surface of the incision in the eye where such surface is in contact with the vibrating ultrasonic needle. This appears to be casually related to the fact that the environmental air is a poor conductor of heat away from the eye and the external tissues are therefore more likely to retain thermal energy transferred from the ultrasonic needle.
It would therefore be desired to provide a degree of cooling to the area of a surgical incision that is more rapid and efficient than that of air cooling to prevent a temperature rise at the incision to a medically unacceptable level during the use of a surgical device.